THE EARLY GROWTH AND DEVELOPMENT STUDY: Using an adoption design to understand family influences and child development
This chapter describes the Early Growth and Development Study (EGDS). The EGDS is a prospective, longitudinal adoption study that was designed to explore the development of adoptive and birth families over time, and to understand the contributions of heritable and environmental processes to child development. The EGDS comprises an adoption kinship network consisting of birth parents, children adopted at birth, and their adoptive parents.
In the first part of this chapter, we present data from the EGDS related to birth parents, as they are a historically understudied population in adoption research. We describe their experiences with the adoption process, including information about events, characteristics, and relationships prior to and following the adoption placement, to provide a comprehensive picture of the short- and long-term impacts of adoption for birth families in the adoption kinship network. Next, we focus on adoptive families and examine how adoption research designs can be a powerful tool for disentangling the effects of the rearing environment on child development above and beyond heritable characteristics and prenatal factors. We additionally summarize key research findings that have emerged from the EGDS over the course of the study and consider implications and future directions for adoption research.
The relationships among heritable and environmental influences on child health and behavior have been studied in many ways, including through adoption designs such as the EGDS and the Colorado Adoption Project (Rhea, Bricker, Wadsworth, & Corley, 2013), through twin designs, and in molecular genetic research. An adoption design featuring birth parents, adoptive parents, and the adopted child is an especially powerful tool for identifying the effects of the rearing environment distinct from the effects of potentially heritable characteristics shared between biological parents and their children. In this chapter, we focus on the EGDS in order to provide an accessible, informative introduction to the benefits of a longitudinal adoption design that includes biological and adoptive parents and the adopted child.
Within a parent-offspring adoption research design, birth parents’ characteristics are used as indicators of heritable tendencies, while birth mothers’ pregnancy experiences and prenatal care are used to characterize their offspring’s prenatal environments. Adoptive parents’ behaviors and features of the adoptive home (e.g., parenting style, marital conflict, sibling relationships, neighborhood characteristics) are used as indicators of the postnatal rearing environment. In this design, the birth and adoptive families are not genetically related. Consequently, similarities between adoptive parent characteristics and the adopted child’s characteristics reflect environmental processes, and similarities between birth parents’ characteristics and the adopted child reflect putative heritable influences and/or prenatal exposures.
A central goal of the EGDS is to understand how family processes influence the expression of children’s heritable predispositions and prenatal exposures over time (Leve, Neiderhiser, Scaramella, and Reiss, 2010). Research in the EGDS reflects four general aims: (1) to examine postnatal environmental influences on child development, (2) to examine evocative gene—environment correlations, (3) to examine gene X environment (GxE) and prenatal X postnatal environment interactions, and (4) to examine longitudinal pathways of continuity and change across development in relation to genetic, prenatal, and environmental influences (Leve et al., 2013). An evocative gene—environment correlation occurs when inherited factors influence children’s rearing environments. For instance, a young child might show an interest in music, and parents might respond by arranging piano lessons for the child or by frequently exposing the child to music. Gene—environment interactions in adoption studies occur when the characteristics of the postnatal environment alter the expression of heritable tendencies (Dick, 2011), or vice versa. For example, genetic factors contribute to children’s risk for becoming overweight or obese. However, a home environment that encourages healthy diets and physical activity could mitigate the expression of this risk. Alternatively, children’s heritable risks for obesity in conjunction with home environments that provide access to unhealthy foods and foster sedentär}' habits could increase the child’s risk for becoming obese. Because the EGDS has followed children over time, it is also possible to examine the impacts of evocative gene—environment correlations and gene—environment interactions on the emergence of new abilities and behaviors in children.
In addition to these study aims, the EGDS also focuses on the adoption kinship network, and has assessed a variety of elements related to adoption, such as characteristics of birth parents and their experience with making an adoption plan. The EGDS has also explored reasons that adoptive parents choose adoption and patterns of openness, and the level of contact between birth and adoptive families.
The EGDS recruited two cohorts, with recruitment beginning in 2003 and ending in 2009. Participating families were recruited with the help of private, licensed adoption agencies or sendee providers who conduct voluntary domestic adoptions across the country (See Figure 7.1).
The EGDS has systematically recruited one of the largest known samples of birth mothers and birth fathers involved in domestic adoption to date, and is one of the largest studies to have recruited “yokes,” a designation stipulating that adoptive families and corresponding birth parents consist of a linked unit connected via the adopted child. The first cohort includes 361 families and the second includes an additional 200 families, for a total of 561 linked units, or yokes.
Following the study’s eligibility guidelines, adoption agencies contacted adoptive families through the mail, and birth parents by phone, to describe the study. Interested individuals were subsequently contacted by EGDS staff for recruitment. Separate staff members contacted the adoptive parents and birth parents in order to maintain a strict firewall, so that information about participation or any other information related to the adoption is never
Figure 7.1 EGDS recruitment sites and volume by state
shared across yoked families by study staff. Leve et al. (2013) provide detailed information about the EGDS recruitment procedures.
Once recruited, birth parents were interviewed in person for the first time three to six months following the birth of the child, and adoptive families were interviewed for the first time by phone when the adopted child was approximately six months old. The adopted children, along with their birth and adoptive families, have been assessed in regular intervals via phone, mail. web. and in-person interviews. The participant retention rates for the sample has exceeded 80 percent over the past 10—15 years. While historically considered a difficult population to track, birth mothers and fathers have remained involved in the EGDS, providing a rich window into the lives of birth parents.